Purpose/Significance of Application:Field demonstration of in situ biosolids and lime treatment of mine tailing deposits contaminated with heavy metals, including cadmium, copper, lead, manganese, and zinc.

Regulatory Requirements/Cleanup Goals:
The goals of the field demonstration were to 1) reduce metals bioavailability, 2) increase the pH of the tailings, and 3) promote vegetation.

Results:The application of biosolids and lime:
- Did not appear to dilute the COC concentrations in the tailings; no consistent trend in COC concentrations was observed before and after treatment.
- Appeared to reduce the availability of COCs, based on a decrease in extractable metals in treated tailings, including water leachable, exchangeable, weak acid extractable, TCLP, and MEP metals in treated tailings.
- Appeared to improve soil quality, based on an increase in pH, TOC, water holding capacity, total nitrogen, phosphorous, and chloride, as well as percent saturation in cation exchange capacity by potassium and sodium after treatment.
- Increased plant and soil microbial activity based on the high biogeochemical activity of the treated soil.
- Reduced soil toxicity, based on the results of plant and earthworm assays.
- Reduced the dietary exposure risk for higher trophic organisms, based on the results of several preliminary dietary exposure models.

Cost Factors:The total cost for the one-year field demonstration was $3,477,697. This cost included $1,738,750 for investigation and characterization and $1,738,947 for construction and cleanup.

Description:Mining operations at the California Gulch Superfund Site, located in Leadville, Colorado, resulted in the release of large volumes of mine waste and acid mine drainage. California Gulch was placed on the National Priorities List (NPL) in 1983, and the primary contaminants of concern (COCs) at the site are cadmium, copper, lead, manganese, and zinc. The site is divided into 12 operable units (Ous). This report focuses on a field demonstration conducted at OU 11, the Arkansas Floodplain, where tailings have been deposited into and along the banks of the Upper Arkansas River.

Biosolids and lime were added to several tailing locations in a one-year study (July to August 1998). The biosolids used in the study were EPA Class B anaerobically digested cake with a solids content of 17%. Tailings were treated at a rate of 100 dry tons per acre of biosolids cake and 100 tons per acre of 3/8" agricultural grade lime. The results of the one-year study indicated that this treatment:
-- Did not appear to dilute the COC concentrations in the tailings; no consistent trend in COC concentrations was observed before and after treatment.
-- Appeared to reduce the availability of COCs, based on a decrease in extractable metals in treated tailings, including water leachable, exchangeable, weak acid extractable, TCLP, and MEP metals in treated tailings.
-- Appeared to improve soil quality, based on an increase in pH, TOC, water holding capacity, total nitrogen, phosphorous, and chloride, as well as percent saturation in cation exchange capacity by potassium and sodium after treatment.
-- Increased plant and soil microbial activity based on the high biogeochemical activity of the treated soil.
-- Reduced soil toxicity, based on the results of plant and earthworm assays.
-- Reduced the dietary exposure risk for higher trophic organisms, based on the results of several preliminary dietary exposure models.
EPA indicated that additional investigation will be needed to evaluate the long-term effectiveness of this treatment. The results of the study were not statistically significant. EPA attributed this to the small sample size and wide variation in results.

The total cost for the one-year field demonstration was $3,477,697. This cost included $1,738,750 for investigation and characterization and $1,738,947 for construction and cleanup.